The present invention relates to an improvement in the oxidation-cleavage processs for preparing resorcinol from m-dialkylbenzene such as m-diisopropylbenzene (m-DIPB). The basic steps of the process and the reactions which occur throughout the process are given in the following prior art references: Britton et al, U.S. Pat. No. 1,934,656; Palfreeman et al, U.S. Pat. No. 2,130,151; Rodgers, U.S. Pat. No. 2,748,172; Great Britain Pat. No. 723,454; Great Britain Pat. No. 724,224; Great Britain Pat. No. 805,048; Great Britain Pat. No. 910,735; Japanese Pat. No. 172,351; and the paper by A. R. Graham (The Distillers Chemicals and Plastics Ltd. Great Britain) entitled "The Production of Resorcinol by the Oxidation of m-Diisopropylbenzene," presented at the Seventh International Meet, World Petroleum Congress, April, 1967.
In the first stage of the process, m-DIPB is oxidized to a mixture of m-diisopropylbenzene monohydroperoxide, m-diisopropylbenzene dihydroperoxide, and other by-products. The second stage of the process consists of extracting and separating the dihydroperoxide and certain impurities from the monohydroperoxide and other impurities. The monohydroperoxide-containing phase is then treated and re-cycled to the oxidizer. The dihydroperoxide-containing phase is treated and subjected to acid catalyzed rearrangement or cleavage in a substantially anhydrous organic solvent consisting of acetone or mixtures of acetone and methyl isobutyl ketone (MIBK). Small quantities of strong acids, normally sulphuric acid, are used as the catalyst. It is important to choose conditions for carrying out the cleavage at high rates and low acid concentrations to minimize loss of yield by the further reaction of resorcinol and acetone to form resins, a process which is also acid catalyzed.
Since the m-diisopropylbenzene dihydroperoxide contains m-diisopropylbenzene hydroxyhydroperoxide as an impurity, the acid catalyzed change results in a mixture comprising acetone, MIBK if used, resorcinol, m-isopropylolphenol (from the m-diisopropylbenzene hydroxyhydroperoxide), and other impurities.
The next stage of the process consists of separating and removing the resorcinol as a high purity product. This is accomplished by neutralizing the rearranged product mixture, removing the volatile solvent and thereafter separating the resorcinol from the impurities.
Thus, in the article by A. R. Graham cited previously, the cleavage product was neutralized to a pH of 3.5-4.0 and steam distilled to remove the volatile solvent. The kettle temperature was then raised, and at temperatures between 200.degree. C. and 300.degree. C., resorcinol and by-product phenols were steam distilled and adducts were cracked. Resorcinol-isopropenylphenol adducts were cracked in superheated steam at about 250.degree. C. The distillate was collected in a mixture of toluene and water. The resorcinol dissolved in the aqueous phase from which it was isolated by azeotropic dehydration with toluene and crystallization from the toluene solution. The by-products m-isopropylphenol and m-isopropenylphenol and dimers of the latter dissolved in the toluene phase. This process results in a resorcinol product which is impure due to the presence of the impurity m-isopropylolphenol. The m-isopropylolphenol, which is present as an impurity in the rearranged cleavage product, is volatile to nearly the same extent as resorcinol and is water soluble. This, it is distilled along with the resorcinol and accumulates in the aqueous phase with the resorcinol.
Other potential methods of recovering a good yield of resorcinol of satisfactory purity include fractional distillation under vacuum; however, this process causes decomposition of the m-isopropyolphenol to m-isopropenylphenol and water. The water forms azeotropes and/or causes, in effect, a steam distillation. In either case, the distillation equilibrium is upset, the desired separation is not achieved, and the overhead product is water wet. In addition, there is, at times, an exothermic reaction which is believed to result from the polymerization of the m-isopropenylphenol, or its alkylation reactions with resorcinol, itself or other impurities.
Treatment of the volatile solvent-free rearranged cleavage product with a liquid which is a solvent for the majority of the impurities and a poor solvent for resorcinol, such as toluene, also does not remove the m-isopropylolphenol since the solubility of the latter and resorcinol are similar.
Thus, there is a need to improve the oxidation-cleavage process for preparing resorcinol from m-dialkylbenzene such that the resorcinol obtained is free from any m-hydroxyalkyl phenol, e.g. m-isopropylolphenol.